Sidan 72fact, the distribution of the ablaut grades in the recorded languages does not
often conform to the principles just laid down. Thus Skt. sthltis, Gk. orAo.is, Lat.
acc. statim < pIE *stdtis 'act of standing', contain only two zero-grade vowels,
neither ...

Sidan 74Metathesis in the Ablaut Grades. In pIE, wf and v>l A before consonants were
subject to metathesis, giving ru and lu, with resulting change of the ablaut series
of the root. This is at the base of the variation quattuor < *-twor-, quartus ...